Linearity - players' point of view

I'm beginning this thread here as a place to continue discussion of pitch linearity... there have been places on the forum where it has be covered before, but instead of continuing to interject on unrelated threads, it would be better to center the discussion in one new location.   

Please theremin players, join... this is where we will talk about...  Pitch Linearity on the theremin, why it is important or why it is unnecessary. I think everyone will come to agreement that the technical design of the theremin is a result of the wishes of the theremin player. however, if there is not enough feedback from a lot of players... the engineering behind new designs could perhaps not be considering everything. no stone should go unturned, eh? 

engineers welcome, but I think this thread would better serve everyone if we could hear more impressions/feedback/opinions from people who play the instrument regularly.

From the thread labeled "'Tanks' for Nothing!" with regard to linearity, coalport wrote:  "I don't think it would do much to make the instrument significantly easier to play because the reason it is hard to play in the first place has nothing to do with the fact that theremins are not perfectly linear. "

I disagree with this statement. The lack of tactile feedback means that the only feedback that is offered is the resulting sound. Therefore, a player learning the instrument must use only the resulting sound to determine all the relationships between their movements (changes in capacitance) and the resulting sound (the pitch).  If the relationship was as close to 1:1 as possible, then the technical foundation of the player can be formed that can be better relied upon, which further facilitates the development of the aural feedback system of the player (listening, correcting errors.) The muscle groups in the body, arm, hands, and fingers can then be developed to perform with higher efficiency with more consistency and reliability.

The challenge of the theremin is in most cases not actually the theremin.  It is derived from players' awareness of their own movements, and their ability to extract meaningful data from their interaction with the theremin in order to form good efficient habits in technique. the limitations for each person are different for because each person has a different level of awareness of all the variables involved with the capacitance/pitch equation. (from the point of view of movement).

a more linearity interaction, IMO, is one significant improvement in the theremin playing experience that can help reduce the confusion a player has when first learning (or for developing to some high degree.) for an instrument where nothing is given to the player, could we at the very least give a player the possibility of establishing a one to one ratio between distance moved and change in pitch ?

I am passionate about this subject for one reason... I have myself experienced, first hand, the benefits of a linear interaction.  when a theremin is easier to play, so much more is possible.

Here is my opinion (as a not very good theremin player, but a player anyway) :)

Playing the theremin on pitch is indeed difficult and would still be difficult even with a perfectly linear field, due to having no feedback other than the sound itself. But I think good linearity definitely helps. If I know that if I open my hand from position 1 to position 4 at any point in the range I'm going to get a 4th, playing is slightly easier than if I have to adapt to the fact that the notes are closer to each other in the higher octaves. Mind you, I do adapt and it comes quite naturally with practice, but it's one more little thing to add to all the other little things that the mind is busy with when playing the theremin. Freeing up even 5% of the mind and devoting it to another task should help, shouldn't it?

(I am still not able to do a consistent vibrato while I'm playing the fastest/hardest parts of songs because my mental CPU usage hits 100% - at that point, it seems that I need to stop doing something - either I do the vibrato or I play (within my limitations) on pitch, but not both).

I suppose perfect linearity is impossible because it depends as much on the player's stance and movements as on the theremin itself, but I think engineers should at least try to make theremins as linear as possible. It's definitely something that I view as an important point for choosing a theremin.

Ok, I was politely asked by the powers that be not to provide information in the other thread that might benefit the future of theremin design. Sometimes I think some members of the theremin community take pleasure in the idea the theremin should be difficult to play and how it works shrouded in mystery.

When I use the term linear I mean all the interval widths are the same. If you spread each musical note width to be ~ ¾” it would match the piano keyboard note for note in repeating distance. This is the phenomenon and not something I invented, it is just the way it is. When the pitch field is linear the outside low notes play the same crisp vibrato as the inside high notes. Name me someone who would not want that?

Vibrato at 55 hz   bellavabro.mp3  My EWS - I don’t hear well enough to play a melody.

The meaning of Electrode: a conductor, through which a current enters or leaves a nonmetallic medium, such as an electrolytic cell.

My Lev Antenna has no direct wire connection and the medium is water. I will stop using the word Lev if someone proved to me he was unaware of what I attempt to describe. Then just call my electrode Bella and know ten years ago as it is documented I might have discovered something beautiful.

Christopher

I'm a terrible player (mainly, I trust, because I haven't practiced / studied enough to get any good) so I hope I'm not barging in here.

I imagine most good players know what pitch linearity is, but for the less experienced IMO the easiest way to observe the effect of non-linearity is to make the same easily repeatable hand gesture at several playing locations and compare the results.  Stand (or perhaps better: sit) at a normal playing distance and null the Theremin pitch.  I would recommend the open hand / closed fist as the gesture, with the open hand fingertips 1" or "2 (or so) away from the pitch antenna as the first playing location (the near-field).  For the second playing location try locating the hand roughly 1/2 way between the pitch antenna and your body (the mid-field).  And for the third location locate the hand very near your body, but still between your body and the antenna (the far-field).  It might help to use a visual (guitar) tuner or similar as an aid in defining the note intervals if your ear isn't well trained in doing this.  Try to keep your body immobile throughout (though of course I realize that movement of the body is a valid playing technique).

I could be way off-base as I only have experience with my (almost certainly mistuned) EWS and my digital prototypes, but I think a properly tuned and nulled Theremin should give very similar pitch interval response throughout a broad mid field, with gradually more cramped response (i.e. more pitch variation for the same hand gesture) the more the playing hand moves into the near and far fields.

"I am passionate about this subject for one reason... I have myself experienced, first hand, the benefits of a linear interaction.  when a theremin is easier to play, so much more is possible."  - randy george

"I suppose perfect linearity is impossible because it depends as much on the player's stance and movements as on the theremin itself, but I think engineers should at least try to make theremins as linear as possible. It's definitely something that I view as an important point for choosing a theremin."  - AlKhwarizmi

I completely agree.  I believe that linearity is important for the obvious expansion of the easy playing area, and also to make the Thereminist less nervous about approaching the antenna.

But I also can't help but believe that non-linearity would be much less of an issue if all Theremins somehow had the option to quickly and easily adjust pitch offset and note spacing (and without negatively impacting mid-field linearity).  If the player could shift and size the pitch range to match their playing style and to better suit the piece they are playing, they could just "hang out" in the mid-field where uncorrected linearity is generally fine. 

I imagine many Theremins that are deemed "difficult to play" simply have overly cramped note spacing in the mid-field (i.e. are overly "sensitive" in the kHz/pF sense).

"I have myself experienced, first hand, the benefits of a linear interaction."  - randy george

I'm curious randy, where have you experienced more linear Theremins? 

Is it with the EW Pro?  I'm also curious as to your (and anyone else's) impressions of the linearity of the EW Pro.

Most people here have probably already seen the following linearity comparison chart that I made a few years ago, comparing the Ethervox, RCA, Etherwave and Etherwave Pro theremins, based on an 18 inch playing arc. 

The Etherwave I used (which I have since given away) was an old model which I built from a kit back in '96. Modern Etherwave theremins may have quite different configurations.

It is my opinion that as far as linearity is concerned, what makes a theremin easier to play is not the evenness of the spacing between notes but the number of notes within the playing arc. The greater the theremin's range, the more notes you have crammed into the same space control area, and the harder the instrument will be to play accurately and consistently.

Of the instruments in this chart, I find the easiest one to play by far is the RCA, with a range of only three and a half octaves. 

"The problem with many thereminists today is that they are too greedy." Clara Rockmore

http://www.peterpringle.com/linearity2.jpeg

The Etherwave Pro is the only instrument which I have experienced this excellent linear interaction of which I've described.  After the past year of studying this particular aspect of the theremin, I am inclined to think that linearity plotted on a graph is only useful to the person who created the graph.

I can speak much more about my theories. I just don't want to write it all in one post because there is a lot to be said.

From the players side of the equation, I have isolated two variables: 1) Proximity of the hand (towards the pitch antenna) and 2) overall capacitance (defined by the total surface area of the players body, including any objects connected to the body, for example sitting on a chair, and also to some degree the capacitance of the surrounding walls, ceiling, floor, air)

The proximity variable can be detected easily. it's the theoretic 'overall capacitance' variable that is the mysterious one because it is unique to each player/environment.  In my opinion, it has been a huge mistake for the second variable to be omitted from the equation, but a huge problem exists, as it is very difficult to measure this value.

As I understand now, there are two equations that must be balanced in order to obtain a linear interaction.  The theremin must first first respond to changes in capacitance in a linear function... this is, of course, a result of the great work of the engineering of a theremin circuit. However ... A second equation must also yield a linear response in order for the theremin to actually produce the linear change in pitch that was intended by the engineering. The second (what seems to be unconsidered) equation is:  the change in capacitance created by a linear difference of the hand position changing in proximity against the overall capacitance value.

This is the reason I believe the theremin cabinet design has an effect on linearity... not because it has anything to do with what goes on inside the theremin, but because it affects the external equation as the physical material in the cabinet becomes part of the changing capacitance value.  This means that at any give location of the hand in the field, all materials at the same proximity are averaged into the capacitance value.  not only that, but anything connected to these objects (within a given proximity) also have an influence : the human body attached to the arm, and the room capacitance to a lesser degree.

I had a very deep discussion of all these topics with Dan Burns, and we agreed on all points. Most of his B3 theremins have a retractable antenna.   With the B3 that I owned I experimented quite extensively with this added variable.  In the end I was able to tweak the pitch response to achieve a two octave portion of the range that offered the kind of linearity that I wanted. i tuned the total playable range to be about 3.5 octaves, but only the inner two gave me the linear response. the full range was actually 6 octaves, but due to the physical size of the range I wanted, the outermost 2.5 octaves were extremely non-linear.

My hypothesis, is that I balanced out the two equations (the internal, and external) by adjusting the antenna's surface area.

If the surface area of the pitch antenna can be defined to a greater degree, as was/is the case with the Henk theremin, it offers a way to balance out the equation on the theremin player side in a larger space.  This is my impression of what happens.  There could be some other logical conclusion, but because I experienced the same effect on the B3, it is the conclusion I have arrived to.

With the Henk, there is a much bigger antenna, extendable to a greater degree...  What I imagine is happening is that : the person/environment has an overall capacitance at rest (meaning no moving objects, nothing changing) and the surface area of the antenna dictates what that value will be... the greater the surface area, I would think, would yield a higher capacitance value from the environment.  

the obvious values to measure have traditionally been proximity of the hand, and resulting change in pitch. But I think perhaps that because the overall capacitance values and antenna surface area are difficult to measure it may not be easy to place them into an equation.

I made a crude diagram that I used to help explain these concepts to the engineer in Seattle that I am working with.  I'll redraw it for readability and post here soon...   I also have thrown a new variable into the mix in the player side equation... I get into that in another post.

I have more to share, but I think I need to know if what I've said already makes sense from an engineering point of view. please share impressions, dewster, chobbs, FredM, Thierry, Christopher, or whom ever wants to jump in.

Clara Rockmore spoke of "thereminists today" from her period of time. Her statement does not apply in 2013, while we are in a time of great accessibility, where there are more than enough passionate individuals who are pushing the envelope to extend what has previously been possible.  I stopped listening to much of Clara's advice because IMO if she were here today, she wouldn't be saying such things.

"http://www.peterpringle.com/linearity2.jpeg"  - coalport

Thanks for that coalport!  (Or should I call you Peter here at TW?)

I have that picture in my Theremin folder but forgot about it until you just reminded us:

Your chart means a lot more to me now than when I first saw it.

"It is my opinion that as far as linearity is concerned, what makes a theremin easier to play is not the evenness of the spacing between notes but the number of notes within the playing arc. The greater the theremin's range, the more notes you have crammed into the same space control area, and the harder the instrument will be to play accurately and consistently."  - coalport

This I totally believe.  Linearity, particularly near the antenna, is a good goal, but wider note spacing with easily changed frequency offsets (e.g. the EW Pro octave shifts) would make the best Theremin IMO.  Control over the note spacing would satisfy both the special effects crowd (who likely want more notes) and the precision player crowd (who likely want fewer notes with offsets).

"From the players side of the equation, I have isolated two variables: 1) Proximity of the hand (towards the pitch antenna) and 2) overall capacitance (defined by the total surface area of the players body, including any objects connected to the body, for example sitting on a chair, and also to some degree the capacitance of the surrounding walls, ceiling, floor, air)

The proximity variable can be detected easily. it's the theoretic 'overall capacitance' variable that is the mysterious one because it is unique to each player/environment.  In my opinion, it has been a huge mistake for the second variable to be omitted from the equation, but a huge problem exists, as it is very difficult to measure this value."  - randy george

The bulk antenna capacitance with an idealized environment is pretty easy to calculate given its physical dimensions.  There are of course stray capacitances associated with the antenna drive, some of which is parasitic in the EQ coil.  But as you say, the bodies of the player and Theremin itself certainly come into play here, as does the the playing environment, humidity, temperature, etc. and some of these elements can be fairly ambiguous and variable.  "That Glasgow Paper" contains a bulk antenna capacitance equation that is pretty good IMO.  The hand | body capacitance was quite a bit harder for me to find a good equation for, but the one in my spreadsheet (with some fiddling) seems to fit the limited actual data I gathered, and it also seems to have some correlation to physical reality which is comforting, but I haven't subjected it to enough real data to confirm it's predictive abilities (particularly with smaller diameter antennas).

The more surface area the antenna has the more capacitance it will have with the environment.  Beyond that I think it's better to fall back on the antenna | hand equations and the design of the oscillator in order to say what will happen with the response when the antenna geometry is changed.  Not to start any fights, but this is one of the reasons I think it is best to make the oscillator as simple (and as sensitive) as possible and deal with all this crap via post processing.  Otherwise (unless you null your Theremin via antenna length or similar) any compensatory circuitry will likely be mistuned by the environment.